1. Field of the Invention
The present invention relates generally to the indication of resource allocation information in a packet data mobile communication system, and in particular, to a method and apparatus for transmitting/receiving resource allocation information through a bitmap.
2. Description of the Related Art
In a general packet data mobile communication system, a base station performs scheduling during every slot or Transmission Time Interval (TTI), or during multiple slots, to determine to which terminal the base station will allocate which resources during the corresponding slot, and then transmits the resource allocation information over a shared control channel or a data control channel. The resources are subject to change according to system operation. For example, the resources can be code resources such as Walsh codes in a Code Division Multiple Access (CDMA) system, frequency band resources in a Frequency Division Multiple Access (FDMA) system, sub-carrier resources in an Orthogonal Frequency Division Multiple Access (OFDMA) system, and time slot resources in a Time Division Multiple Access (TDMA) system. Because the sub-carriers belong to frequency, both the sub-carrier resources and the frequency band resources will be referred to herein as frequency resources.
It is possible for a system to support all of the CDMA, FDMA, OFDMA and TDMA systems. In this case, the resources can include all of codes, frequencies, and time slots. In the following description, it should be noted that the resources refer to all or some of codes, sub-carriers and time slots according to system configuration.
A detailed description of the shared control channel will now be made. A base station performs scheduling during every slot, and transmits over the shared control channel an indicator indicating to which terminal the base station will allocate which resources during the slot according to the scheduling result. Although the scheduling is achieved herein for every slot for convenience, the scheduling can also be performed every several slots. The scheduling result information included in the shared control channel can include various control information for other functions supported by a particular system, in addition to the information indicating to which terminal the base station allocates which resources.
The control information as used herein refers to the information indicating to which terminal the base station allocates which resources. Each of the terminals (active terminals in reality) in the system demodulates the shared control channel transmitted by the base station every slot, determines whether there are resources allocated thereto at this slot, and transmits/receives data using the allocated resources if there are resources allocated thereto.
An indicator indicating to which terminal the base station will allocate which resources is generally implemented using a terminal identifier and a resource allocation identifier. That is, it is assumed that all terminals in the system have their own unique identifiers, and the code and frequency resources also have unique identifiers according to a predetermined regular rule. For example, it is assumed that the terminal identifier is expressed with 10 bits, and the amount of resources included in one slot is 12. Generally, the amount of resources allocated to a terminal having the terminal identifier is transmitted with 12 bits over the shared control channel together with the 10-bit terminal identifier using a bitmap scheme. That is, for 12 resources, the indicator indicates using a bitmap whether to allocate each of the resources.
Assuming that N terminals are simultaneously scheduled to an arbitrary slot, N×(10+12) bits are needed to transmit/receive resource allocation information using a bitmap. However, the shared control channel, to which Hybrid Automatic reQuest (HARQ) is not applied, is a channel having high (or expensive) overhead, and transmission of the resource allocation information having the large amount of information causes degradation of system performance.